EP-A No.-0001831 filed Feb. 11, 1978 with the same inventors of the present application describes a hairdryer provided with a safety device which, by means of an electronic control and tripping circuit, instantly interrupts electrical feed to the hairdryer should conditions arise--such as the presence of moisture or water on electrically conducting parts--which could cause short-circuiting or, more dangerously, electrical discharge through the user's body.
This device is based on the use--as moisture or water sensing element--of a pair of parallel, slightly spaced-apart metal grids which are electrically isolated from each other and are connected individually to the control and tripping circuit by conductor wires. One pair of grids is disposed in correspondence with each air inlet or outlet aperture of the hairdryer.
The operation of this device is perfect, both with regard to response time and with regard to the certainty of the circuit remaining de-energized and of the electrical feed to the hairdryer remaining cut off for the entire time during which water or moisture is present on the sensing grids.
In the industrial production of hairdryers in accordance with EP-A- No. 0001831, in which the requirement of a high production rate does not always permit maximum care in manufacture, it has however been found that an item of possible risk is the connection between the sensing grids and the control circuit. As stated, each grid is connected to the control and tripping circuit by a fairly thin conductor wire soldered at one end to the grid and at the other end to one of the circuit terminals. If one of these wires should become accidentally interrupted, or if one of the respective soldering points should succumb--which could happen not only during manufacture but also during use--the respective control grid would remain isolated and therefore be no longer able to perform its function.
In DE-A- No. 3122232 is described a device similar to that of EP-A- No. 0001831; however from the very schematic description it is clear that this device has not solved the problem, which is at the base of the present invention.